1. Field of the Invention
The present invention is generally directed to a method and apparatus for the downhole disposal or injection of water in a well using natural gas supply. In particular the present invention uses pressurized gas to operate both a downhole pump used for injection and lift the desired petroleum portion and some water of the produced fluid to the surface.
2. Background
Many hydrocarbon and natural gas producing wells generate water from the same subterranean formation that produce the hydrocarbon and gas. In typical practice, the production fluid, a mixture of both hydrocarbon and water, is pumped or "lifted" to the surface. The water is separated from the hydrocarbon at the surface and the water subsequently treated and disposed of on the surface or reinjected back into a suitable disposal formation.
In wells having sufficient underground pressure within the producing formation, the production fluid is lifted "naturally" and the principle operating cost of the well is the disposal of the water in an environmentally conscious manner. However, there are a significant number of wells in which the underground pressure is not sufficient to lift the production fluid to the surface without pumping or some other artificial lifting of the fluid. The artificial lift may be provided by downhole pumps which require either mechanical (e.g. sucker pumps, progressive cavity pumps), electrical (e.g. electric submersible pumps) or hydraulic connections (e.g. hydraulic turbine centrifugal pumps) to the surface. Another technique often used is "gas lifting" in which compressed gas is used to lift the production fluid to the surface. Gas lifting is typically used in situations where the location of the well does not allow for the use of the other pumping techniques due to a lack of space or infrastructure or other factors. Examples of the gas lift technique can be found in several U.S. Patents including U.S. Pat. Nos.: 5,217,067; 4,251,191; 3,718,407; and the references cited therein, the contents of which are incorporated herein by reference.
When the water cut (i.e. percentage of water) of the production fluid is high, the cost of pumping the production fluid to the surface and the disposal of the water makes the well uneconomical to operate. In gas lifting wells, a high water cut makes the well uneconomical or even impossible to operate because of the operating cost, and the cost and space needed for the equipment required to recover the hydrocarbon and dispose of the water. It such cases it may also be desirable to create downhole water floods, conserve supply gas on the surface, reduce the impact of hydrocarbon production on the environment as well as other benefits that will be apparent to one of skill in the art.
Methods for the downhole disposal of the water contained in production fluid have been recently developed to reduce the cost of operating high water cut hydrocarbon wells. One such method is described in U.S. Pat. No. 5,296,153 in which a cyclone separator is placed downhole to separate the hydrocarbon and water components of the production fluid. The hydrocarbon component is lifted to the surface either naturally or by a mechanical, electrical or hydraulic downhole pump. A second downhole pump is used to dispose of the water component in an underlying porous formation. In order to drive the dual downhole pumps some sort of mechanical, electrical or hydraulic connection to the surface is required. Further, in order for the cyclone separator to be effective, the water cut is limited to 80%. In addition to the capital cost and maintenance required for operation, the size of the existing well casing string may prevent the installation of downhole pumps. Thus, if the well is to remain productive, a new hole must be drilled and a larger casing installed.
Another method for the downhole disposal of the water component of the production fluid is disclosed in U.S. Pat. No. 5,497,832. In the described method, the upstroke of a sucker rod pump is used to lift a fluid mixture of primarily hydrocarbon to the surface. The downstroke of the sucker rod pump is used to inject the remaining water component into a disposal formation.
Using present technology, the use of downhole water separation and disposal in a high water cut well requires a connection from the surface--be it mechanical (e.g. sucker rod or rotating rod string), electrical (e.g. cables) or hydraulic (e.g. hydraulic fluid lines), or other conventional methods geared to use existing infrastructure to drive the downhole pump system. As noted above, gas lift wells are often located in places were the cost and space for such support infrastructure is prohibitive. For example, there are many coastal water hydrocarbon platforms were space is very limited and the provision of electrical power is not possible. When the water cut from these gas lift wells becomes too high, they are either capped and abandoned or idled for production at a later date.